The Berserk skill has been revised-- it previously didn't really fit the feel of being Berserk, since you'd often want to use it out of combat, maybe in between naps. This felt sadly non-Berserk.

The new helpfile:

Syntax: berserk

Only powerful fighters can master berserking, the ability to enter insane
rage in combat. Its effects are not unlike the frenzy supplication -- a
huge surge of combat prowess, coupled with a disregard for personal safety.
Berserking characters are more resistant to the effects of spells, however
they suffer a penalty to the effectiveness of most of their own skills,
spells, supplications, and powers. Being berserk sheds the effects of
minor wounds, temporarily increases the maximum health of the adventurer,
and improves the rate of healing during combat. The ease of compelling
one's mind into such a focused state is impacted by one's morale.

Orcs who use this skill against a powerful enough foe will get a short-lived
burst of additional offense. They will also make an additional attack in
the following combat round, and possibly in subsequent rounds. In general,
the positive effects of the Berserk skill will be more potent for an orcish
berserker.

It is slightly harder to convince oneself to flee when in a Berserk rage,
and the heightened emotions prevent voluntary sleep. Berserk fighters also
have some degree of resistance to being knocked unconscious by physical or
magical means.

Giants have a limited affinity for flying into a rage, and start with
a modicum of skill, even without practicing with their guildmasters.

Syntax: recuperate

By taking a moment to calm the mind and body, one can improve the
healing of wounds, and find more energy to continue adventuring. Wise
adventurers find this ability most useful.

Druids with this skill may only perform it while in wilderness, where they
are at peace.